Xerographic developing apparatus



May 28, 1953 H. E. CRUMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 1'! Sheets-Sheet 1 S. m m V m Herberi E.Crumrine u Charles L. Huber ATTORNEY May 28, 1963 H. E. CRUMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 2 HIGH VOLTAGE POWER SUPPLY SVIl-SV mvszvroa. Herbert E.Crumrine BY Charles L.Huber ATTORNEY I l l FIG. 3

23, 1953 H. E. CRUMRINE ETAL 3,091.219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 3 INVENTOR. Herbert E.Crumr|ne Charles L. Huber ba e? May 28, 1963 H. E. CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 4 K g Q INVENTOR. Herbert E.Crumr|ne BY Charles L.Huber y fi ATTORNEY May 28, 1963 H. E. CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 195'? 1'7 Sheets-Sheet 5 mmvrox Herbert E.Crumrme By Char|,s ;L;Huber 7W TTORNEY "E if E z i May 28, 1963 H. E. CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 6 INVENTOR.

Herbert E.Crumrine BY Charles L. Huber ATTORNEY M y 1963 H. E. CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 1'7 Sheets-Sheet 7 FIG. 9

INVENTORS Herbert E.Crumrme (BY Charles L.Huber TTORNEY May 1963 H- E. CRUMRINE ETAL 3,091,219

XERQGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 8 INVENTOR Herberi E.Crumrine y Charles L.Huber zmrfi ATTORNEY May 28, 1963 Original Filed June 3, 1957 I I 335 1 Q} I "a u POWDER CLOUD sv GENERATOR IO H. E. CRUMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS l7 Sheets-Sheet 9 PR URIZED 445 IR CLEANER EXHAUST MAN I FOLD SUPPLY MANIFOLD DUST COLLECTOR EXHAUST FIG. 11

IN V EN TOR.

Herbert E.Crumrine BY Charle; L.Huber ATTORNEY May 28, 1963 H. E. CRUMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 1'7 Sheets-Sheet 10 FIG. 13

INVENTOR Herbert E.Crumrine BY Charles L. Huber ATTORNEY M y 28, 1963 H. E. CF'UMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheets-Sheet 11 INVFNTOR. Herbert E. Crumrme y Charles L. Huber May 28, 1963 H CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 uvmvrox Herbert E.Crumr|ne BY Charles L.Huber 7 M T'ToRNEY 17 Sheets-Sheet 12 y 8, 1963 H. E. CRUMRINE ETAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 1'? SheetsSheet 13 mmvrox Herbe rf E. Crumrine Charles L. Huber H. E. CRUMRINE ETAL XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 May 28, 1963 I3 ACTUATED TC 0'. n 9

h ACTUATED w l3 RELEASED a RELEASED sw n2 ACTUATED l4 nausea Ia ACTUATED w|1 RELEASED a; R 39 w m RELEASED w :4 ACTUATED l2 RELEASED w a ACTUATED SW15 RELEASED 5W l6 RELEASED TIMER 1 SW I5 ACTUATED TC 4; R 14 CLUTCH SOLENOID V AIR CYLINOERB SOLENOID VALVE 2 4 TIME IN SECONDS FIG. 0

BY M'%/MTORNEY 1'? Sheets-Sheet 14 5w l6 ACTUATED T a (1-4 $EQOEL.)

INVENTOI Herbert E.Crumrine Charles L.Huber y 8, 1963 H. E. CRUMRINE EIAL 3,091,219

XEROGRAPHIC DEVELOPING APPARATUS Original Filed June 3, 1957 17 Sheds-Sheet 15 SHIN.

'6 INVEFYTOR Herbert E. Crumrine Charles L.Huber Y E N 3:330. R ".3 0 523mm: 0 W :tnJua N A 3:201: w E N E mm T flfllufl 1 M 3:3 n2 Bo us-i Y 9:3 I B Jumofixow 0 M y 1963 H. E CRUMRINE ETAL 3,091,219

mocmmc DEVELOPING APPARATUS Original Filed June 3, 1957 1'? Sheets-Sheet 16 HHHHHHHHI H lNTERYkLOMETER FIG. 22

JNVENTOR. Herbert E.Crumrine BY Charles L. Huber ATTORNEY May 28, 1963 H. E. CRUMRINE ETAL 3,091,219

' XEROGRAPHIC DEVELOPING APPARATUS Original' Filed June 3, 1957 17 Sheets-Sheet 17 nvvzszvron. Herbert E. Crumrine Charles L.Huber FIG. 23

United States Patent Oi -cc Original application June 3, 1957, Scr. No. 663,085. Divided and this application Dec. 24, 1958, Ser. No.

4 Claims. (Cl. 118-637) This invention relates to the field of xerography and, particularly, to improvements in automatic xerographic processing equipment for forming direct xerographs.

In the process of xerography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1952, a xerographic plate comprising a layer of photoconductivc insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrosta'tically charged, finely divided material, such as an electioscopic powder, which is brought into surface contact with the photoconductive layer and is held thereon electrostatically in 'a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface to which it may be fixed by any suitable means.

Following the disclosure of the basic electrophotographic or xerographic techniques in the Carlson patent, many improvements have been made in xerographic plates and developing materials to increase plate sensitivity and .panchromaticity and to improve resolution of the final image structure. In addition, many improvements have been made in each of the component devices for effecting xerographic processing, i.e., in devices for electrostatically charging xerographic plates, in devices for exposing such plates, in apparatus for developing electrostatic latent images, in xerographic powder image transfer devices, and in powder image fixing devices. For the most part such improvements have been employed in apparatus for reproducing line copy images, and such devices are presently in wide commercial use for this purpose. However, the additional complexities involved in forming continuous tone images by xerographic techniques has heretofore hindered the application of such techniques to the field of direct photography.

The principal object of this invention is to improve automatic xerographic processing equipment to provide a compact, high speed, and light weight apparatus for forming dlnect positive, continuous tone xerographs, particularly for use in aircraft. A further object of the invention is to minimize the time delay between the sensitization of a xerographic plate and the development of an electrm static latent image formed thereon. A further object of the invention is to extend the time period between successivc uses of indivlual xerographic plates employed in automatic xerographic processing equipment. A further object of the invention is to maintain a xerographic processing apparatus free of accumulated developing powder during operation. A further object of the invention is to improve xerographic plate handling devices to permit rapid, uniform and positive movement of a rigid xerographic plate through an automatic xcrographic processing apparatus. A further object of the invention is to improve xerogrsphic plate storage devices to permit repetitive processing of successive xcrographic plates scriatim. A further object of the invention is to improve xerographic developing apparatus whereby the xerographic developing op- 3,091,219 Patented May 28, 1963 er-ation may be effected in a sealed chamber and wherein the development electrode surface may be cleaned between developing operations. A further object of the invention is to improve xerographic plate charging devices for forming a uniform electrostatic charge on a xerographic plate surface. A further object of the invention is to improve xerographic plate positioning devices for maintaining a xerographic plate in the focal plane of a lens system. A further object of the invention is to improvexerographic plate cleaning mechanisms for removing residual powder from xerographic plates in transit. A further object of the invention is to improve apparatus for transferring xerographic powder images from xerographic plates to a support surface.

These and other objects of the invention are attained in a preferred embodiment which comprises a self-contained, fully automatic, xerographic system that is intended for use in an aircraft for producing successive, continuous tone, aerial xcrographs under the control of an intervalomcter. Essentially, the apparatus includes a magazine assembly for storing xerograph-ic plates, a charging assembly for forming a uniform electrostatic charge on the photoconductive surface of each plate, a lens and shutter assembly for making exposures, a development assembly for developing the latent images on the plates, a printing assembly for transferring developed images to a continuous paper strip, brush cleaning devices for removing residual developing powder from the xerographic plates and the development electrode of the developing assembly, and plate handling and control devices associated with these assemblies to form a completely integrated and fully automatic system.

In operation, xerographic plates are fed seriatim from the magazine to an exposure position and, in transit, each plate is charged by a scorotron or screened corona discharge device that places a uniform positive electrostatic charge over the surface of the plate. The plate is then passed to an exposure position wherein it is exposed in conventional manner to form a latent pattern of electrostatic charges thereon that corresponds to the subject of the exposure, and is then transported to a development chamber wherein it is positioned adjacent to a development electrode. Development is effected by a negatively charged developing powder that is injected into the chamher from a powder cloud generator connected thereto, the powder particles being electrostatical-ly attracted to the positive charge pattern formed on the plate. When development is complete, the chamber is scavenged by low pressure air to remove developing powder suspended in the air of the chamber. The chamber is then partly opened, and the plate is advanced to feed rolls that pass it through pressure rolls in conjunction with a continuous, adhesive-coated, paper strip whereby the powder image formed on the plate is transferred to the adhesive strip. Once the plate is clear of the developing chamber, the chamber is reclosed and scavenged with high pressure air to eliminate residual powder, and the development electrode is cleaned by a brush assembly that is actuatedthrough a clutch that forms part of the development chamber assembly. After leaving the pressure transfer rolls, the transfer paper with the powder image thereon is passed through a second set of pressure rolls conjointly with a transparent plastic web which adheres to the adhesivc on the transfer strip and fixes the powder image thereon by forming a protective cover thereover.

Simultaneously, the plate is passed to a pivotable direction-changing mechanism having plate driving rolls frictionally driven from a drive roll geared to the transfer pressure rolls. Plate holding rolls retain the plate within the direction-changing mechanism as it is pivoted about its axis to engage the driving rolls with a second drive roll that reverses the direction of rotation of the plate driving rolls. On engagement with the second drive roll, the plate is withdrawn from the direction-changing mechanism and is advanced through a cleaning position wherein residual powder is dusted therefrom by a cleaning brush which, in turn, is cleaned of residual powder by a fiicking bar. Suitable vacuum means are provided to remove this residual powder from the machine. After passing through the cleaning position, the plate is gripped by another set of drive rolls and is returned to the magazine wherein it is deposited on top of the other plates therein for reuse.

A preferred form of the invention is disclosed in the appended drawings, in which:

FIG. 1 is a schematic perspective view of the xerographic camera system of the invention as adapted for installation in an aircraft;

FIG. 2 is an enlarged perspective view of the several components of the xerographic camera system of the invention;

FIG. 3 is a functional schematic cross-sectional view of the xcrographic camera and processing apparatus;

FIG. 4 is an isometric view of a xerographic plate adapted for use in the invention;

FIG. 5 is an isometric view of the xerographic plate magazine assembly, with side walls broken away, illustrating the several plate actuating mechanisms therein;

FIG. 6 is an isometric view of the plate transfer mechanism and plate charging mechanism;

FIG. 7 is a detail sectional view of the xerographic plate latching mechanism of the plate transfer mechanism;

FIG. 8 is an isometric view, partly in section, of the exposure position mechanism of the invention;

FIG. 9 is an isometric view, partly in section, of the developing mechanism of the invention, showing the several components thereof substantially in extended position to withdraw a xerographic plate from the exposure position mechanism;

FIG. 10 is a side elevation of the developing mechanism of the invention, showing the several component parts thereof in retracted position for developing a xerographic plate;

FIG. 11 is a schematic diagram of the pneumatic system of the invention, and includes a schematic cross-sectional view of the major components of the developing mechanism, as well as a schematic isometric view of a portion of the exposure position mechanism;

FIG. 12 is a sectional view illustrating the structural arrangement for electrically isolating a xerographic plate held in the developing mechanism assembly;

FIG. 13 is an isometric view of the direction-changing mechanism;

FIG. 14 is an isometric view of the xerographic powder image transfer mechanism and the image fixing mechanism;

FIG. 15 is a schematic sectional view of the mechanisms of FIG. 14;

FIG. 16 is an isometric view, partly in section, of the xerographic plate brush cleaner mechanism;

FIGS. 17 and 18 are detailed sectional views, respectively, of the left and right hand structural arrangements for supporting the xerographic plate cleaning brush of FIG. 16;

FIG. 19 is a schematic isometric view, partly in section, of the drive mechanism of the invention;

FIGS. 20 and 21, taken together, constitute a timing chart of an operational cycle of the mechanism of the invention;

FIGS. 22 and 23, taken together, constitute a wiring diagram of the several electrical control circuits of the invention;

FIG. 24 is an isometric view of the powder cloud generating mechanism;

FIG. 25 is a side elevation of a powder cloud generating assembly; and

FIG. 26 is a sectional view of the powder outlet assembly of the powder cloud generating assembly.

In the particular embodiment shown in the drawings (see FIGS. 1 and 2) the invention is adapted for installation in an aircraft, and is shown as comprising a xerographic camera 10, containing a lens and shutter mechanism as well as all xcrographic processing equipment; a control unit 20, wherein the several pneumatic and electrical control circuits of the system are housed; and an intervalometer 30, for initiating operation of the system. The camera and processing mechanism is preferably housed in a cast magnesium cover assembly 11 that is separable substantially at its mid-section to permit access to the interior of the apparatus. Within the housing, two spaced side plates or frames are integrally connected by tie rods to form a rigid framework for supporting the several components of the xerographic processing equipment.

On the front wall of the exterior of housing 11 there is located a power-driven, takeup roll spindle 12 for storing aerial xerographs 13 taken and processed by the apparatus. A lever 14 is providsd to actuate a web cutter inside the housing, whereby finished xerographs may be detached from those in process. Manually settable knobs 15 and 16 project through an opening 17 to permit adjustment of the diaphragm and speed-setting mechanisms, respectively, of the lens and shutter assembly of the camera. On the lower portion of housing 11 there are provided two trunnions 18, at the front and rear of the camera, whereby the camera portion of the system may be sup ported on the inner gimbal ring 19 of a gyroscopic stabilizing system which, together with an outer gimbal ring 21, is pivotally supported in a shock-mounted frame 22 within the aircraft. By the latter means the xerogiaphic camera is maintained in a proper attitude with reference to the ground for taking aerial xerographs by means of suitable gyroscopically controlled servomotors (not shown) that function to compensate for pitching, rolling and yawing motions of the aircraft.

For actuating the several components of the camera mechanism, a plurality of electrical, pneumatic and vacuum lines 24 connect camera 10 to control unit 20 which, in turn, is connected to the aircraft electrical and pneumatic supplies via a plurality of lines 25. Housed within the control unit is an electrical circuit unit 26 including relay circuits for controlling the various automatic and interlocking functions of the several componcnts of the camera apparatus, a pneumatic control system unit 27 for controlling the operation of a plurality of high pressure air systems and vacuum' systems essential to the proper functioning of the camera mechanism, and a dust filter unit 28 for removing xerographic developing powder from air exhausted from the system. A plurality of control knobs and switches 29 are provided on electrical circuit unit 26 for conditioning the system for automatic operation and for testing the several components thereof in accordance with prescribed maintenance requirements. Intervalometer unit 30 is connected to control unit 20 via a cable 31 and is provided with a plurality of setting knobs 32 whereby the camera apparatus may be conditioned for taking single exposures or successive exposures in timed relation, in accordance with conventional aerial photography practice.

The relative arrangement of the several components of the interior of the xerographic camera and processing apparatus are best shown in the schematic sectional view of FIG. 3 wherein a lens and shutter assembly 40 is mounted over an opening in the lower end of housing 11 in a manner to form a light-tight seal with the housing. Assembly 40 includes a lens system 41, a diaphragm 42 which is settable under con-trol of knob 15, as described above, and a shutter mechanism (not shown) that may be cocked and released in accordance with conventional practice in aerial photography.

For forming xerographlc images, the system is provided with a plurality of xerographic plates 50 (see also FIG. 4), each of which comprises a conductive backing plate, preferably of brass, having a photoconductive layer 51, preferably of amorpl: nus selenium, formed on one face thereof. Each plate 50 is provided with two side rails 52 that are integrally secured thereto and are so constructed to position the plate with reference to the several mechanisms with which it cooperates, and to form a recessed area for photoconductive iuyer 51 to protect a xerographic. powder image formed thereon from smearing during transit of the plate through the system.

Prior to their use in the system, a supply of xerographic plaiacs 50 is manually inserted in a magazine assembly 100 which is then placed in the camera wherein it is supported on suitable guide rails (not shown) formed on the framework of the apparatus. From the magazine, plates 50 are passed seriatim over a charging mechanism assembly 200, whereby the photoconductive surface of each plate is given a uniform electrostatic charge, and is then passed to an exposure position mechanism 230 wherein each plate is held momentarily during the exposure period. During exposure a charge pattern or electrostatic latent image, corresponding to the subject being xerographed, is formed on each plate. After exposure, the plate is passed to a development mechanism assembly 320 wherein the electrostatic latent image of the subject is converted to a xerographic powder image thereof. After development each plate is passed through an image transfer assembly 470, whetcin its xcrographic powder image is transferred to an adhesive support surface, and thence to a direction-changing mechanism 490, whereby the plate is aligned with and passed through a brushcleaning apparatus 540 wherein residual powder remaining on the photoconductive surface of the plate is removed. After cleaning, the plate is returned to magazine assembly 100 for reuse.

Plate Magazine The plate magazine comprises a self-contained, lighttight, box-like structure wherein a plurality of xerographic plates are loaded preparatory to use in the system. Preferably, the magazine is of such construction to prevent the admission of light, and is provided with a dark slide covering t e bottom opening thereof when the magazine is removed from the camera. When the magazinc is placed in position in the system it cooperates with the framework of the machine in a manner such that a light-tight structure is maintained when the dark slide is removed. As an integral part of the magazine structure there is provided a plate spacing and advancing mechanism that is actuated by a motor through a single-revolution clutch, whereby plates fed to the magazine are retained in their respective positions and are released singly from the bottom of the magazine for use in the system. Also forming a part of the magazine structure is a plate transfer mechanism actuated by an air cylinder, whereby plates in the magazine may be withdrawn seriatim and be advanced to the plate charging apparatus.

Specifically, plate magazine assembly 100 (see FIGS. 3 and 5) includes a box-like casting having a cover portion 101, side walls 102 and 103, a front wall 104 and a rear wall 105 that forms a rear cover plate for the camera. and is provided with suitable bosses and interior wall portions for supporting the several components of the magazine mechanism. Before the megazine is inserted in the camera, a supply of xerographic plates 50 is placed there n. The plates are inserted in the magazine through a rectangular opening 106 in front wall 104, with photoconduetive layer 51 facing downwardiy, end are adapted to be supported within the magazine by four interponent members 107, one of which is fixed on each of two pairs of shafts 108 and 109 arranged on opposite sides of the magazine. Each of the shafts 108 is rotatably mounted in a bearing 110 set in cover portion 101 and a bearing block 111 tixed on the respective side walls 102 and 103. Similarly, each of the shafts 109 is rotatably mounted in a bearing 112 and a bearing block 113.

On the right-hand side of the magazine (as shown in FIG. 5) each of the shafts 108 and 109 has IiXCd thereto a helical gear 115 that meshes with a similar helical gear 116 fixed on a shaft 117 that is provided a one end with a bevel gear 118 that is driven by a bevel gear 119 fixed on a tubular sleeve 120 that is rotatably mounted in a vertical wall portion 121. Similarly, shafts 108 and 109 on the left-hand side of the magazine are provided with helical gears 123 that mesh with gears 124 fixed on a shaft 125 that is provided with a bevel gear 126 that meshes with a bevel gear 127 fixed on a tubular sleeve 128 that is rotatably mounted in a vertical wall. portion 129. Tubular shafts 120 and 128 form part of a single-revolution clutch mechanism 130, described be low, whereby power from the drive mechanism of the camera is transmitted via a sprocket 132, shaft 133, pinion 134, gear 135, shaft 136, and the clutch mechanism to effect intermittent rotation of the shafts 117 and 125 whereby xerographic plates may be released from interponent members 107, as described below.

For supporting xerographic plates after they are released by interponent members 107, t" i i n a members 138 and 139 are provided on each side of the magazine, each of which is pivotally suspended from an associated block 140 that is secured to the inner face of the side walls 102 and 103. Each of th hook members is resiliently urged inwardly against the plates in the magazine by a suitable spring (not shown) and is provided with a hook portion that underlies the lowermost plate in the plate stack when the parts are in the position shown in FIG. 5.

The single-revolution clutch mechanism 130 is an adaptation of a conventional form of single-revolution clutch such as that used in the shutter winding mechanism of the K-l7 aerial camera. Briefly, it constitutes a solenoidactuated device which, upon energization of the solenoid, serves to engage the several operating mechanisms of the magazine with a constantly rotating shaft, during a single revolution thereof, to effect the required actuation of such mechanisms. As shown in FIG. 5, the clutch mechanism includes a pair of side plates and 146 that are held together for unitary movement by pins 147 and are fixed respectively to sleeves 120 and 128 which are rotatably mounted on drive shaft 136. In the space between side plates 145 and 146, there is a ratchet 148 that is fixed on drive shaft 136 and rotates constantly therewith. Cooperating with the ratchet 148 is a ratchet pawl 149 that is pivotally mounted on a stud 150 extending between the side plates, and is resiliently urged into engagement with the ratchet by a three-armed lever 152 that has a lug extending over a tail portion of ratchet pawl 149 and is resiliently connected to the ratchet pawl by a spring 153 that is extended between a stud on the lever and a stud on the pendant end of the ratchet pawl. The entire pawl and lover assembly is resiliently urged clockwise about stud 150 by a spring 154 extended between the upwardly extending end of lever 152 and a stud secured on side plate 146. When the clutch mechanism is disengaged, as shown in the drawings, ratchet pawl 149 is held out of engagement with ratchet 148 by a holding pawl 155 that underlies a forward extension on ratchet pawl 149. The upper end of holding pawl 155 is pivotally mounted'in a bracket 156, that is secured to the underside of cover portion 101, and is pivotally. connected at its midportion to a spring-urged armature 157 of a solenoid SOL-X, that is also secured on cover 101.

When the clutch is inactive, the several parts thereof remain in the position shown so that ratchet 148 rotates freely with drive shaft 136. When the clutch is to be activated, solenoid SOL-X is energized, thereby drawing armature 157 inwardly against the tension of its spring and disengaging holding pawl 155 from ratchet pawl 149. 

1. AN APPARATUS FOR DEVELOPING ELECTROSTATIC LATENT IMAGES ON XEROGRAPHIC PLATES INCLUDING A BASE PLATE ASSEMBLY HAVING INLET AND OUTLET CONNECTIONS FOR XEROGRAPHIC DEVELOPING MATERIAL, A DEVELOPMENT ELECTRODE ASSEMBLY INCLUDING A DEVELOPMENT ELECTRODE AND HAVING INLET AND OUTLET CONNECTIONS FOR DEVELOPING MATERIAL THAT ARE ALIGNED WITH THE CORRESPONDING CONNECTIONS OF THE BASE PLATE ASSEMBLY, MEANS ON SAID DEVELOPMENT ELECTRODE ASSEMBLY FOR SECURING A XEROGRAPHIC PLATE THEREON IN OPERATIVE RELATION TO THE DEVELOPMENT ELECTRODE, MEANS FOR MOVING THE DEVELOPMENT ELECTRODE ASSEMBLY INTO AND OUT OF OPERATIVE RELATION WITH THE BASE PLATE ASSEMBLY, MEANS OPERABLE WHEN THE DEVELOPMENT ELECTRODE ASSEMBLY IS OUT OF OPERATIVE RELATION WITH THE BASE PLATE ASSEMBLY FOR POSITIONING A XEROGRAPHIC PLATE ON THE DEVELOPMENT ELECTRODE ASSEMBLY, AND MEANS OPERABLE WHEN THE DEVELOPMENT ELECTRODE ASSEMBLY IS IN OPERATIVE RELATION WITH THE BASE PLATE ASSEMBLY FOR MAINTAINING SAID OPERATIVE RELATION FOR A PREDETERMINED TIME PERIOD. 